Method for making a disposable face respirator

ABSTRACT

A PROCESS OF SIMULTANEOUSLY FORMING AN ATTACHING THE FILTER MEDIUM TO THE FACE PIECE IS ALSO DISCLOSED. THE PROCESS COMPRISES DEPOSITING A FIRST THIN LAYER OF SOLIDS FROM AN AQUEOUS SLURRY ONTO A FORAMINOUS SUCTION MOLD HAVING THE SURFACE CONTOURS DESIRED FOR THE INTERIOR OF THE FILTER MEDIUM, PLACING A FACE PIECE HAVING AN INTEGRALLY FORMED APERTURED LIP OFER THE MOLD AND THE FIRST LAYER, DEPOSITING A SECOND THIN FIBROUS LAYER OF SOLIDS FROM AN AQUEOUS SLURRY ON THE OUTSIDE SURFACE OF THE FIRST LAYER, ON THE OUTSIDE SURFACE OF THE APERTURE LIP AND WITHIN THE APERTURES IN THE LIP. IN A PREFERRED PROCESS, TWO FIBROUS BACKING LAYERS ARE PROVIDED IN THIS MANNER AND A FIBROUS FILTER LAYER IS DEPOSITED FROM AN AQUEOUS SLURRY ON THE OUTSIDE SURFACE OF THE SECOND FIBROUS BACKING LAYER AND WITHIN AN UNDERCUT AREAS PROVIDED IN THE APERTURED LIP. AN ADDITIONAL FIBROUS PROTECTING LAYER IS PREFERABLY DEPOSITED ON THE OUTSIDE SURFACE OF THE FILER LAYER FROM AN AQUEOUS SLURRY.

Jan. 15, 1974 G. P. REIMSCHUSSEL L 3,736,125

METHOD FOR MAKING A DISPOSABLE FACE RESPIRATOR Original Filed March 4, 1971 2 SheetsSheet 1 Jan. 15, 1974 p REWSCHUSSEL ETAL 3,786,126

FOR MAKING A DISPOSABLE FACE RESPIRATOR METHOD 2 Sheets-Sheet 2 Original Filed March 4,, 1971 3,786,126 METHOD FOR MAKING A DISPOSABLE FACE RESPIRATOR George Paul Reimschussel, Flemington, NJ., and Jacob Matthys Prins, Sinking Spring, Pa., assignors to Johns- Manville Corporation, New York, N.Y.

Original application Mar. 4, 1971, Ser. No. 121,086, new Patent No. 3,688,768. Divided and this application July 24, 1972, Ser. No. 274,366

Int. Cl. B28b 1/26 US. Cl. 264-87 7 Claims ABSTRACT OF THE DISCLOSURE A process of simultaneously forming and attaching the filter meduim to the face piece is also disclosed. The process comprises depositing a first thin layer of solids from an aqueous slurry onto a foraminous suction mold having the surface contours desired for the interior of the filter medium, placing a face piece having an integrally formed apertured lip over the mold and the first layer, depositing a second thin fibrous layer of solids from an aqueous slurry on the outside surface of the first layer, on the outside surface of the aperture lip and within the apertures in the lip. In a preferred process, twofibrous backing layers are provided in this manner and a fibrous filter layer is deposited from an aqueous slurry on the outside surface of the second fibrous backing layer and within an undercut area provided in the apertured lip. Anadditional fibrous protecting layer is preferably deposited on the outside surface of the filter layer from an aqueous slurry.

This is a division of application Ser. No. 121,086, filed Mar. 4, 1971, now U.S. Pat. 3,688,768 granted Sept. 5, 1972.

BACKGROUND THE INVENTION Field of the invention DISCUSSION OF THE PRIOR ART Face respirators have been used for. many years in environments which are particularly noxious or unpleasant. In order to efficiently filter out fine dust and fibers, face respirators have often been quite elaborate in construction, consisting of cumbersome face pieces, special replaceable elements or inserts, breathing valves to facilitate inhalation and exhalation, and often other elements of special design and purpose.

While elaborate respirator designs, which often tend to be heavy, have been thought to be necessary for effective filtration in dust and fiber laden environments, the discomfort experienced in wearing some respirators for a substantial length of time has often caused workers to ignore them and to continue breathing unfiltered air.

Recently, it has beenproposed to provide light weight, disposable, face respirators, that are intended for use only for a limited period of time, such as one day, and which are subsequently thrown away. Such face res irators are described in copending patent application, Ser. No. 112,364, for Disposable Face Respirator by Thomas Joseph Weeks, Jr. and George PaulReimschussel filed Feb. 3, 1971, and assigned to the assignee of this application. These masks are produced by forming the filter "United States Patent 3,786,126 Patented Jan. 15, 1974 medium on'a mold having the desired shape from aqueous fiber slurries and then joining the preformed filter medium to the face piece.

Disposable face masks to be economically feasible must be inexpensive so that a new one can be Worn frequently. Thus, it is important to provide a relatively simple, rapid and inexpensive technique for producing these masks. It is further important to provide a mask which is disposable, efiicient, comfortable to wear and has a low breathing resistance. These masks should also prevent unfiltered air from by-passing the filter medium and entering the respiratory system of the wearer.

OBJECTS OF THE INVENTION An object of this invention is to provide an improved inexpensive, disposable face respirator which functions efficiently and limits the amount of unfiltered air inhaled by the wear.

Another object of this invention is to provide an improved disposable face respirator which is comfortable to wear and which provides effective filtering performance.

An additional object of this invention is to provide an improved, relatively simple, rapid and inexpensive process for manufacturing such a respirator.

These and other objects will be apparent to those skilled in the art from the description which follows and from the drawings.

SUMMARY OF THE INVENTION This invention provides an inexpensive, disposable and efficient face dust mask which is comfortable to wear and which reduces the amount of unfiltered air inhaled by the wearer by including an efiicient filter medium to face piece sealing joint. This invention also provides a rapid, inexpensive procedure which eliminates the previous intermediate step of joining the face piece to the preformed filter medium. The process produces an efficient filter medium to face piece sealing joint in a face mask which has the desired properties.

The provision of an effective filter medium to face piece sealing joint prevents passage of air between the face piece of the mask and the filter element. An efficient sealing joint is necessary to permit the mask to operate in its intended manner.

An improved filter medium to face piece sealing joint is provided in a respirator mask, which includes a shape retaining filter medium formed of a plurality of fibrous layers that cover a major portion of the; surface area of the mask and a flexible face piece attached to the periphery of the filter medium. The face piece has a facesealing band at its outer periphery which is conformable to the contours of a wearers face for preventing passage of air between the face piece and the wearers face. The improved joint extends around the periphery of the filter medium and comprises an apertured lip integral with and extending around the internal periphery of the face piece. A first fibrous layer of resin-bonded, interfelted resilient fibers contacts the inside surface of the apertured lip in a laminar relationship and a second fibrous layer comprising interfelted resilient fibers contacts the outer surface of the apertured lip also in a laminar relationship, with the fibers in the second layer extending into the apertures and contacting fibers in the first layer to hold the apertured lip in interlocking relationship between the first and second layers.

In a preferred embodiment, the apertured lip intersects the face-sealing band in an acute angle along a line spaced from the inner periphery of the band to provide an undercut area in which fibers which form the filter layers of the filter element can be drawn to provide a good seal between the filter element and the face mask. In this preferred embodiment the filter medium includes two fibrous backing layers and a filter layer. The fibrous backing layers comprise resin-bonded interfelted resilient fibers, the first backing layer contacting the inside surface of the apertured lip and the second backing layer contacting the outer surface of the apertured lip, with the fibers in the second backing extending into the apertures and engaging fibers in the first backing layer to hold the apertured lip in interlocking relationship with the first and second backing layers. The filter layer overlies and contacts the second backing layer and extends into the undercut area formed at the intersection of the apertured strip and the facesealing band.

The invention also provides an improved, relatively simple, rapid and inexpensive process for manufacturing such a mask. An improved method of joining a filter medium and a face mask is provided in a process for producing a respirator mask of the type in which a fibrous filter medium comprises a majority of the surface area of the mask, and a face piece is attached to the periphery of the filter medium. The process of this invention eliminates the prior intermediate step of joining the preformed filter medium to the face piece while at the same time providing an improved sealing joint. The improved method of joining the filter medium and the face piece comprises providing a flexible face piece including a marginal faceengaging outer peripheral band and an inner peripheral portion that comprises an apertured lip; depositing on a foraminous suction mold having the surface contours desired for the interior of the filter medium a first thin fibrous layer of solids by drawing an aqueous slurry comprising resilient fibers and a binder material to the foraminous mold and passing water from the slurry through the foraminous mold; placing the face piece over the foraminous mold and the first layer with the inner sur face of said apertured lip in contact with said first layer; depositing on the outside surface of said first layer and on the outside surface of the apertured lip and within the apertures in the apertured lip a second thin fibrous layer of solids by drawing an aqueous slurry comprising resilient fibers and a binder material to the foraminous mold and passing water from the slurry through the apertures in the apertured lip, the first layer and the foraminous mold to hold the apertured lip between the firts and second layers and in interlocking relationship therewith. A fibrous filter layer of solids is thereafter similarly deposited on the second fibrous layer. Preferably, a protective fibrous layer of solids is then deposited on the filter layer. The filter medium is then cured to set the binder either while on the mold or after its removal from the mold.

The apertured lip structure formed integrally with the flexible face piece enables the simultaneous formation of the filter medium and attaching of the filter medium in interlocking relationship with the apertured lip. The invention helps reduce the cost of manufacturing the mask and the resulting mask is inexpensive enough so that it can be discarded after, for example, only one day of use for optimum comfort and protection of the user.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of one embodiment of the respirator mask in use on a wearers face;

FIG. 2 is a perspective view of an embodiment of the mask showing the face piece and the apertured lip without the filter medium;

FIG. 3 is a perspective view of another embodiment of the respirator mask showing an alternative arrangement of the face piece and of the apertured lip without the filter medium;

FIG. 4 is a cross section of the embodiment shown in FIG. 1 taken on the line 4-4 looking in the direction of the arrows; and

i 4 a FIG. 5 is a schematic representation, shown partly in section, of apparatus used in a preferred method for forming the respirator mask.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the drawings, wherein like characters designate like or corresponding parts throughout the several views, a respirator mask is illustrated in FIG. 1 and includes a flexible face piece 10 and a shape-retaining filter medium 12.

Face piece 10 is manually deformable so that it can be conformed to the human face and has an upper edge portion that is recessed to receive the bridge-0f the wearers nose. A face-sealing band 14 forms the outer periphery of face piece 10. The respirator mask fits over and covers the users nose and mouth and is held in placed by mating pairs of elastic bands 16 and 18 having end fasteners 20 attached thereto as seen in FIG. 2.

An aperture lip 22 is provided that is integral with and extends from face piece 10. Apertured lip 22 includes a plurality of quadrilateral apertures 23 and circular apertures 24 as best seen in FIGS. 2 and 3. The circular openings are spaced from sealing band 14 and the quadrilateral apertures are positioned adjacent the sealing band. Facesealing band 14 of face piece 10 includes a first continuous surface 26 (FIG. 4) that extends into apertured lip 22. The band 14 also includes a second surface 28 that intersects lip 22 at an acute angle that opens outwardly away from the interior of the mask. An undercut area is formed between lip 22 and surface 28. This undercut area extends around the periphery of the face piece 10 and helps provide a good sealing joint.

The large quadrilateral openings 23 permit fibers in the filter medium to be drawn into the undercut area during the forming of the filter medium to provide a good seal between face piece 10 and filter medium 12. The diameter of openings 24 preferably is at least inch. Details of this process will be described later in the specification.

Face piece 10 can be formed of a variety of elastomeric materials and synthetic resins which can be molded to provide a resilient face piece, including for example, synthetic rubbers such as styrene-butadiene rubber, and such synthetic resins as polyvinyl chloride. The material selected should be nontoxic and nonirritating to human facial tissue.

The filter medium is formed of at least two fibrous layers that are formed in overlying relat ionship with one layer on each side of the apertured screen lip. Preferably, the filter medium includes two backing layers, and a filter layer in overlying relationship with one of the backing layers.

The exterior surface of filter medium 12 is convex so that the top portion starts adjacent the face and extends downwardly while curving outwardly away from the face to extend over the nose. The bottom portion of the mask curves downwardly and inwardly toward the chin of the wearer as shown in FIG..1.

Because the filter medium forms the major part of the respirator mask and preferably forms almost the entire surface area of the mask, it must be strong enough to withstand the rigors of wear, handling and abuse, and yet flexible enough to yield when manually deformed by the wearer or by pressure applied by elastic bands 16 and 18 that extend around the back of the wearers head, to conform the face piece to his face. These criteria require that a flexible binder be incorporated in the filter medium to bond the fibers together. Also, the binder is needed to provide the mask with the desired strength and resistance to abrasion.

With reference to FIG. 4, a preferred embodiment is illustrated in which filter medium 12 includes first and second backing layers 32 and 34. First backing layer 32 contacts the inner surface of apertured lip 22. The peripheral portions of second backing layer 34 contact the outer surface of apertured lip 22 and fibers in second backing layer 34 extend through apertures 24 to contact fibers in first backing layer 32. The remaining portions of second backing layer 34 overlie and contact the outer surface of first backing layer 32. Layers 32 and 34 securely interlock the aperture screen lip in laminar relationship between them.

The fibers of the backing layers are selected to be coarse enough so that when inter felted by a vacuum molding process they form a fiberous layer containing pores that are too large to become plugged by the amount of binder necessary for adequate strength. Because the backing layers help provide the needed strength, resiliency, and abrasion resistance, no binder or a much smaller amount of binder can then be used in the filter layer. Thus, binder plugging of the filter layer is avoided without interfering with the filtration efficiency of the over-all filter medium.

Backing layers 32 and 34 are each preferably formed of short length A2 inch or less up to about /2 to 4 inch), strong, stiff, and resilient fibers having a resilient waterinsoluble binder distributed over the fibers. Fibers of about /s inch or more in length tend to produce desirable surface corrugations which increase the effective surface area for filtration. Fibers in the backing layers can be of either random or graded lengths. As shown in FIG. 4, filter medium 12 includes a fibrous filter layer 36 in overlying contact with the outer surface of second backing layer 34. Filter medium 12 can further include a fibrous protective layer 38 which is similar to the first and second backing layers and which is comprised of bonded interfelted resilient fibers. Protective layer 38 overlies and contacts the other surface of filter layer 36.

The compositions of the backing layers, filter layer, and the protective layer can be those described in the aforementioned Weeks et a1. application. The disclosure of that application is incorporated herein byreference. Backing layers 32 and 34 and protective layer 38 of this invention are each preferably composed of materials described as capable of being used in the backing layers of the aboveidentified application, while the composition of filter layer 36 is preferably the same as that for the filter layer discussed in said application.

For example, backing layers 32 and 34 and protective layer 38 can be formed of such suitable fibers as rayon, and various synthetic fibers such as acrylics, polypropylene, polyethylene, polyesters and polyamides. Preferably these fibers are of a denier of from less than 1 to about 1.5. Filter layer 36 preferably includes fine diameter fibers and strong, resilient fibers of a larger diameter. If desired, all the fibers in the filter layer can be fine diameter fibers. The fine diameter fibers can be selected from a variety of materials including glass and synthetic organic polymers which can be formed into fibers having desirable properties, such as stiffness, similar to those of glass fibers. These fibers can include polyvinyl chloride, polyamides and polypropylene. Glass fibers are, however, presently preferred. The larger diameter strong, resilient fibers can be selected from those described above for incorporation into the backing and protective layers.

The fibers of the filter layer tend to form a compact interfelted layer having small pores or interstices extending downwardly across the thickness of the layer and distributed throughout the surface area of the filter layer when drawn from a dilute aqueous slurry onto a foraminous mold. The strong resilient fibers are included in filter layer 36 to provide the necessary strength and resiliency and to act as a spacing means to prevent overcompaction of the finer fibers. In one preferred embodiment, the filter layer includes from about 4% to about 20% by weight of the fine fibers. It should be understood that the smaller the average diameter of the finer fibers used, the smaller is the weight percent of these fibers that is necessary to obtain good filtration efiiciency. Also, when fine fibers having larger average diameters are used, larger amounts of the fine fibers can be present without causing excess breathing resistance. For example, when the fine fibers have diameters approaching about 1.6 microns, these fibers can be present in an amount over 20%. When fine fibers of larger average diameters, for example, about 1.6-2.6 microns, and above, are employed, these fibers can constitute of the fibrous portion of the filter layer.

As illustrated in FIG. 3, the respirator mask can include an exhalation valve (not shown) which is fitted into aperture 51, although the filter medium itself usually permits comfortable exhalation. Suitable exhalation valves are commercially available; for example, inexpensive flapper valves can be used.

The invention also provides an improved process of forming a respirator mask. The process eliminates an intermediate step required in presently known manufacturing procedures for forming respirator masks including a face piece and a filter element by simultaneously forming the filter medium and securing the filter medium to the face piece of the mask.

In accordance with the process of this invention, a flexible face piece having a marginal face-engaging outer peripheral band and an inner peripheral portion that comprises an apertured screen lip is provided. A first thin fibrous backing layer of solids is deposited on a foraminous suction mold having the surface contour desired for the interior of the filter medium by drawing an aqueous slurry comprising resilient fibers and a binder material to the foraminous mold and passing water from the slurry through the mold. Then, the face piece and the apertured screen lip are placed over the foraminous suction mold and a second thin fibrous backing layer of solids is deposited on the outside surface of the first backing layer and on the outside surface of the screen lip in the same manner by drawing an aqueous slurry comprising resilient fibers and a binder material to the foraminous mold. FIG. 4 illustrates the relationship of first backing layer 32, face piece 10, and second backing layer 34. Water from the slurry is passed through the first backing layer, the apertures in the screen lip and the foraminous mold to sandwich the lip 22 between the first and second backing layers.

Subsequently, a filter layer of solids is deposited on the second backing layer from an aqueous slurry by drawing the slurry to the foraminous mold and passing water from the slurry through the first and second backing layers and the foraminous mold. Preferably, a protective layer is subsequently deposited on the filter layer. The protective layer is comprised of resilient fibers and a binder material as in the first and second backing layers. Deposition of the protective layer is also accomplished by drawing an aqueous slurry comprising resilient fibers and a binder material to the foraminous mold and passing water from the slurry through the first and second backing layers, the filter layer and the foraminous mold.

As shown in FIG. 5, a plural dip vacuum forming technique is preferably used in the manufacture of the respirator mask filter medium and in the attachment of the filter medium to the face piece. Although positive pressure could be applied to the aqueous slurry to create the pressure drop across the mold, a vacuum forming technique is preferred as described below.

In FIG. 5, the vacuum forming technique utilizes a tank 46 which contains a first fibrous slurry 48, a second tank 50 which contains fibrous slurry 52 having the same composition as that of slurry 48 and a third tank 54 that contains a third fibrous slurry 56 having a different composition from that of slurries 48 and 52. Although separate tanks 46 and 50 are illustrated, it should be understood that a single tank having the composition of slurries 48 and 52 therein could also be used. A foraminous mold 60 is attached to an airtight carrier 62 to which a conduit 64 is connected. The conduit connects the interior space between mold 60 and carrier 62 to a source of vacuum which is applied through the conduit to the interior surface of the mold when the mold is immersed in the fibrous slurry 48. The vacuum causes passage of the liquid in the slurry through mold 60 and the deposition of solids from the slurry 48 on the mold. It is this deposition of solids on the mold that forms first fibrous backing layer 32 for the mask.

After a layer of solids of a desired thickness has been deposited to form first backing layer 32, face piece 10 is placed over the mold with continuous surface 26 located adjacent to the mold and with the interior surface of lip 22 in contact with backing layer 32. Mold 60 is then inserted into fibrous slurry 52 in tank 50 while maintaining the interior of the mold and carrier structure under suction. Alternatively, mold 60 may be reinserted into slurry 48 when slurry 48 is identical in composition to slurry 52. Another vacuum forming operation is then carried out in tank 50 to provide second fibrous backing layer 34. This layer is formed over the first backing layer 32 and is formed on the outside surface of apertured screen lip 22. It is during this step and the succeeding steps of the process that the undercut area between apertured lip 22 and second surface 28 is important. Deposition of the second backing layer is accomplished by drawing an aqueous slurry 52 comprising resilient fibers and a binder material to the foraminous mold 60 and passing water from the slurry through first backing layer 32, the apertures 24 in screen lip 22 and the foraminous mold to sandwich the screen lip between first and second backing layers 32 and 34. The peripheral areas of second backing layer adhere to the outside surface of lip 22 and to first backing layer 32 through apertures 24 to produce a strong interlocking and laminar configuration. As a result, the filter medium is formed and simultaneously attached to the lip 22 of face piece 10. As the solids are being deposited on the outside surface of apertured screen lip 22, the space between the lip and second surface 28 enables the solid materials or fibers to be drawn into the space to effect a good seal between face piece 10 and apertured screen lip 22. Thus, the undercut area enables the solid materials to collect within the space to form the seal desired. If desired, a bead of cement (not shown) may be applied within the space or a heat-seal technique may be used to further insure retention of a good face piece to filter medium seal. The remaining portions of second backing layer 34 adhere to the outer surface of first backing layer 32.

Following the deposition of second backing layer 34, conduit 64, carrier 62 and mold 60 are removed from tank 50 and mold 60 is inserted into fibrous slurry 56 in tank 54 while maintaining the interior of the mold and carrier under suction. Another vacuum forming operation is then carried out in tank 54 which comprises fine diameter fibers to provide filter layer 36 which is formed over second backing layer 34. The filter layer is deposited by drawing slurry 56 to the foraminous mold 60* and by passing water from the slurry through the first and second backing layers and the foraminous mold. Again, the undercut area between surface 28 and apertured screen lip 22 permits solid materials to be deposited therein. The deposi tion of solids in this area provides a good seal between face piece 10 and apertured screen lip 22.

Preferably, a protective layer 38 is deposited on filter layer 36. This is accomplished by moving conduit 64, carrier 62 and mold 60 back to tank 50 and immersing the mold into slurry 52 for another vacuum deposition step. The mold is then removed from tank 50 and the filter medium is preferably cured at an elevated temperature to set the binder either while on the mold or after removal therefrom. The filter medium can be cured while on the mold by maintaining the vacuum and inserting the mold covered with the face piece and the fibrous layers into a hot air chamber, such as a drying oven. The hot air is drawn through the fibrous layers and the foraminous mold thereby permitting rapid setting of the binder material. Very short cure times of, for example, about 10 to 30 seconds can be achieved. If it is desired to cure the filter medium after removal from the mold, subsequent to removal from tank 50, the vacuum is discontinued and positive air pressure is applied to the conduit to remove the face piece and the fibrous layers formed on the outer surface of the mold. The filter medium is then heat cured.

It should be understood that in most cases fibers from a layer being deposited extend somewhat into the pores or interstices of a previously deposited layer, with the layer being deposited overlying the previously deposited layer.

The exterior surface of foraminous mold 60 is shaped to have the dimensions of the desired interior surface of the filter medium. The mold can be made from any suitable porous material such as, for example, highly porous ceramic material such as firebrick, or a fine mesh screen.

As set forth in the aforementioned Weeks et al. application, it is desirable that the aqueous slurries be very dilute to ensure that the solids in the slurries remain uniformly distributed throughout. Solids concentrations of from about 0.015% to about 0.03% by weight based on the total weight of the slurry are preferred. Also, the amount of the pressure differential applied across the forming mold is a factor in determining the speed of the molding operation and has some effect on the characteristics of the deposited fibrous layers. Generally, for dilute slurries the pressure differential across the mold for depositing the first fibrous layer is from about 1 to about 10 inches of mercury. The pressure differential is usually increased for each succeeding layer, since the deposited layers act as a filter cake. As the thickness of the deposited solids increases, the filtration rate is slowed. It should be understood that the desired pressure differential across the mold depends on several factors including the porosity of the mold, and the porosity of the first formed layers, and the nature of the slurry. Thus, under some circumstances, it may be desirable to use pressure drops above or below the above-cited range.

For a clearer understanding of the mask construction and the methods of making the mask, specific examples are set forth below. These examples are illustrative, and are not to be understood as limiting the scope and underlying principles of the invention in any way. All percentages listed in the specification and claims are weight percentages unless otherwise noted.

EXAMPLE 1 A flexible face piece having an apertured lip is formed of a thermoplastic elastomer, sold by Shell Chemical Company under the trade designation Kraton, by injection molding. The face piece has the configuration illustrated in FIG. 2. The filter medium for the respirator mask is vacuum-formed on a porous firebrick mold. The mold is shaped to the desired form, and a rubber diaphragm is cemented to the back of the mold to allow application of a vacuum. The filter medium is formed by initially dipping the mold under a vacuum of about one inch of mercury into a first backing layer slurry and drawing the solids to the mold to form the first backing layer. The integrally formed face piece and apertured lip are then placed over the mold and the mold is then dipped into a second backing layer slurry to form the second backing layer. Subsequently, the mold is dipped into a filter layer slurry, and the mold is finally dipped into a protective layer slurry, to form, respectively, the filter layer and the protective layer. Thereafter, the vacuum is released and the filter medium and the face piece are blown off of the mold by positive air pressure.

The slurry used to form the first and second backing layers and the protective layer contains fine denier, high tenacity rayon fibers and binder. The slurry used to form the filter layer contains fine glass fibers, high tenacity rayon fibers and some binder. The aqueous slurries used to form each of the layers are prepared in S-gallon quangallons of each-slurry on the mold.

egrsalze 9 titie Each respirator mask is formed by depositing The slurry'compositions'used in forming the "respirator mask are shown below:

Slurry for backing layers and Slurryror protective filter layer layer %-}6 in. lengths of random-cut high tenacity rayon fibers (a product of Celanese sold under the trademark Fortisan") having diameters of about 10 microns, gms- 6. 6. 00 1.6-2.6 micron diameter glass fiber (a prodnot of Johns-Manville Corp. sold under the trademark Micro-Fiber), 3. 51 0.5-0.75 micron diameter glass fiber (a product of Johns-Manville Corp. sold under the trademark Micro-Fiber"), gms.-...'. 1. 27 Acrylic resin binder (50% solids by weight) (a product of B. F Goodrich Chemical Co. sold under the trademark Hycar #2600x120), ml. '10 3 1 M NaOH, ml 200 100 Water Suflicrent to give 5 gallons of slurry The fiber constituents are added to the slurries from concentrated stock suspensions having the following concentrations:

Fortisan rayon fibers 1.5 gm./650 ml. 1.6-2.6 micron Micro-Fiber glass fiber 0.4 gm./ 100 ml. 0.5-0.75 micron Micro-Fiber" glass fiber 0.25 gm./ 100 ml.

When tested, the resulting respirator mask permitted only a very low percentage of dust to pass through the mask.

EXAMPLE 2 The filter medium is formed on a porous wire screen mold. The surface of the mold has the configuration of the desired interior surface of the mask and the filter medium is formed by the layered deposition of two different aqueous slurries using apparatus similar to that shown in FIG. 5. The working slurry used for forming the backinglayers includes 0.16 gram per liter-of acrylic fibers sold under the trademark Creslan? by American Cyanami'd and designated Type 61. These fibers are 1.5 denier and are normally inch in length. About 0.13 gram per liter of solids from an acrylic latex emulsion (Hycar #2600 x 137) is deposited on the fiber. The backing layers working slurry also contains a smallamount of wetting agent; Sodium hydroxide is added to break the latex emulsion and to deposit the latex on the fiber. Subsequently, the slurry is diluted to the working consistency described above. I For the filter layer, a working slurry is formulated which contains 0.15 9 gram per liter of acrylic fiber .(Creslan Type 61). and 0.041 grams per liter of Micro- Fiber" glass, fibers having a diameter of from 0.5 to 0.75 micron.

The respirator mask is formed by first integrally forming a flexible ,face piece made of polyvinyl chloride and including an apertured screen lip by a conventional injection molding process. A first. backing layer containing about 0.375 grain of fiber and 0.312 grain of binder is deposited on the mold by drawing up 2.37 liters of the backing layr's'working slurry; 1A vacuum ofabout o'ne inchofmercury---is applied across-the mold to draw-up the slurry. Theiiitgrally'formed face piece and' apertured lip areithen placed over the mold and over:the first backing layer with the inside surface of the lip in contact with the first backing layer. A second backing layer is then deposited on the exterior surface of the first backing layer and on the exterior surface ofthe aperturcd lip by drawing an identical amount of slurry through the mold under a vacuum of about two inches of mercury. Subsequently, a filter layer is deposited on the mold and on the outer surfaceof the second backinglayer by withdrawing 4.75 liters of the filter layer working slurry containing fine glass fibers under a vacuum of about 6 inches of mercury. An outer protective layer is then deposited on the outer surface of thefilter layer by withdrawing from the backing layer working "slurry 4.75 liters of slurry under a vacuum of about ten inches of mercury. The filter medium and the face piece are then blown ofi the moldby positive air pressure and held at about C. for about 1 hour to cure the binder.

The present invention provides a uniquely constructed i-respirator mask and a unique processv for manufacturing the mask. The filter medium issimultaneously formed and secured .to a face piece. An apertured screen lip on the face piece ensures the secure fastening ofthe filter medium to the face piece and at the same time eliminatesthe extra 7 step heretofore required in previous manufacturing processes of separately forming and fastening the filte medium to the face piece of the respirator mask. m

It is to be understood that variations and modifications of the present invention may be made without departing from the spirit of the invention. It is also to be understood that the scope of the invention is not to be interpreted as limited to the specific embodiment disclosed herein, but only in accordance with the appended claims when read in the light of the foregoing disclosure.

What is claimed:

j 1. In a process for producing a respirator mask in which a fibrous filter medium comprises a majority of the surfac e areaof themask, and a face piece is attached to the periphery of the filter medium, the improvement comprising a method of joining the filter medium and the a face piece comprisingi providing a flexible face piece including a marginal face engaging outer peripheral band and an inner peripheral portion which includes an aperture lip,

saidaperture lip having inner .and outer surfaces! depositing on a foraminous suction mold having the surface contours desired for the interior of the filter medium, a first thin fibrous layer of solids by drawing an aqueous slurry comprising resilient fibers and a binder material to the foraminous mold and passing water from the: slurry through the foraminous mold;v I (placing the'face piece over the foraminous mold and the first layer with the inner surface of said apertured lip in contact With said first layer; and

depositing on the outside surface of said first layer and on-the, outside surface of .said .apertured lip and .within theapertures in said apertured lip a second thin fibrous layer of solids by drawing an aqueous fiber slurry to the foraminous mold and passing water from the slurry through the apertures in said apertured lip, the first layer and the foraminous mold to hold saidapertured lip between the first and sec- 0nd layers and in laminar contact therewithand curing the filterv medium at an elevated temperature to set the binder.

L 2. The process of claim 1 wherein said second thin fibrous layer is formed from an aqueous slurry' comprisingf resilient fibers and a binder material, and including the step of depositing a fibrous filter layer on the outer surface of said second layer by drawing an aqueous slurry positing on the outer surface on said filter layer a pro:

tective layer comprising resilient fibers anda binder material prior to curing the filter medium.

4. The process of claim 2 in which said apertured lip and the face-engaging band intersect at an acute angle that provides an undercut area and wherein filter layer solids are drawn into and depositedin. said undercut area to provide an efiective seal between the face piece and the filter medium. 1

5. The process of claim 2v wherein a vacuum is used to deposit said layers. 1

.6. The process of claim 1 wherein the filter medium is cured while on the mold by inserting the mold into a hot.

air chamber and drawing hot airthrough the filter medium and the foraminous mold. I

7. The process ofclaim 1 wherein said face piece and said apertured lip are integrally formed by injection molding. References Cited UNITED STATES 'PATENTS 1,910,771 5/1933 Knight 162219 X 3,589,979 6/1971 Finch 162-219 2 l29,431 10/ 1947 Sloan 162---2l9 ROBERT FIWHITE, Primary Examiner T. P. PAVELKQ, Assistant Examiner I us. or. X.R. 162104, 219; 264-250, 255,258, 273 

